The present invention relates to a regenerated collagen fiber having a mercapto group and/or disulfide linkage and a method of manufacturing the same. The regenerated collagen fiber of the present invention has a mercapto group and/or a disulfide linkage and, thus, can be optionally deformed by a redox reaction. In addition, the deformed shape can be retained. Thus, the regenerated collagen fiber of the present invention can be used as a substitute for human hair, animal hair and as a catgut.
In general, the skin or bone of an animal is used as a raw material in the manufacture of a regenerated collagen fiber. The raw material is treated with an alkali or enzyme to decompose and remove the telopeptide portion of the collagen so as to make the collagen soluble in water. Then, the solubilized collagen is spun to prepare a regenerated collagen fiber. The regenerated collagen fiber, which exhibits a high mechanical strength among the protein fibers like silk, is widely used in various fields. Particularly, the regenerated collagen fiber, which is a protein fiber having a characteristic molecular structure, is close to human hair, which is also a natural protein fiber having a very complex fine structure, in draping, luster and feel. Such being the situation, various attempts are being made to use the regenerated collagen fiber for the manufacture of animal hair-like fibers used as a substitute for a human hair and fur.
In general, the cysteine residue and cystine residue within the natural collagen molecule are present in the telopeptide portion. Thus, the regenerated collagen fiber molecule after removal of the telopeptide portion is substantially free from the cysteine residue or cystine residue, making it impossible to apply a permanent wave treatment to the regenerated collagen fiber unlike the human hair. The term "permanent wave treatment" denotes the chemical treatment applied to the human hair in, for example, a beauty salon for modifying an optional shape, which can be retained, to the human hair by utilizing a redox reaction.
For modifying the regenerated collagen fiber, various measures have already been reported including, for example, a chemical modification and a treatment using a metal crosslinking agent. However, an attempt to introduce a mercapto group or a disulfide linkage to the regenerated collagen fiber has not yet been reported. As described previously, the regenerated collagen fiber retains to some extent the molecular structure inherent in collagen. However, the molecules of the regenerated collagen are arranged irregularly. It has not yet been clarified whether or not a permanent wave treatment can be applied to the regenerated collagen fiber of the special fiber structure in the case of introducing a mercapto group and/or a disulfide linkage to the regenerated collagen fiber.
Various synthetic fibers are also proposed for use as a substitute for the human hair. For example, proposed as a synthetic fiber in Japanese Patent Disclosure (Kokai) No. 63-191829 is a polyamino acid having a mercapto group or a disulfide linkage attached to the side chain of the polymer. It is described that a permanent wave treatment can be applied satisfactorily to the particular synthetic fiber. Similarly, a polyamino acid derivative is disclosed in, for example, Japanese Patent Disclosure No. 7-316287. However, each of the synthetic fibers disclosed in these prior arts consists of a limited number of amino acids and widely differs in the fiber structure from the regenerated collagen fiber of the present invention. It should also be noted that these methods for introducing a mercapto group or a disulfide linkage is applied to synthetic fibers which can be subjected to severe reacting conditions and which are prepared from the raw material amino acids which can be obtained easily. Therefore, it was impossible to apply these methods to the regenerated collagen fiber made of natural proteins and, thus, tending to be denatured.